Polly Carmichael became the director of the Gender Identity Development Service at the Tavistock in 2009. “I remember our office was literally a room that had probably been a broom cupboard at one stage”, she recalls. But the decision in 2011 to start offering puberty blockers to under-16s, and in 2016 to widen the professionals who could refer a child to GIDS had a major impact. The numbers of people on the waiting list ticked inexorably up, until the clinic felt it could barely cope.